That would be lms/templates/index.html.
Do you mean the landing page and layout of edx.org? To the best of my knowledge that was never released publicly.
But if you want something different and can afford to wait, I’d keep tabs on the work OpenCraft is doing with its new Open edX theme, which unless I’m horribly mistaken, will likely be released publicly with an open source/creative commons license. Looks like that will be a nice change from the default!